In a typical cellular network, also referred to as a wireless telecommunication system, a wireless device or User Equipment (UE), communicates via a Radio Access Network (RAN) to one or more Core Networks (CNs).
A wireless device is a device by which a subscriber may access services offered by an operator's network and services outside the operator's network to which the operator's radio access network and core network provide access, e.g. access to the Internet. The wireless device may be any device, mobile or stationary, enabled to communicate over a radio channel in the communications network, for instance but not limited to e.g. mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The wireless device may be portable, pocket storable, hand held, computer comprised, or vehicle mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another wireless device or a server.
Wireless devices are enabled to communicate wirelessly with the communications network. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between the wireless device and a server via the radio access network and possibly one or more core networks, and possibly the Internet.
The radio access network covers a geographical area which may be divided into cell areas, with each cell area being served by a base station, e.g. a Radio Base Station (RBS), which in some radio access networks is also called eNB, NodeB, B node or base station. A cell is a geographical area where radio coverage is provided by the base station at a base station site. The base stations communicate over the air interface with the wireless devices within range of the base stations. In the following, the term network node or eNB may be used when referring to the base station.
Multimedia Broadcast and Multicast Services (MBMS) is a broadcasting service offered via cellular networks. The MBMS is a point-to-multipoint service in which data is transmitted from a single source entity to multiple recipients. The MBMS service may be used for file download and for streaming type of services, e.g. “Mobile TV”.
Enhanced MBMS (eMBMS) is an enhanced version of MBMS and it is used to denominate MBMS service in Evolved Packet Systems (EPS) including E-UTRAN (LTE) and UTRAN access. E-UTRAN is short for Evolved UMTS Terrestrial Radio Access Network, UMTS is short for Universal Mobile Telecommunications System, LTE is short for Long Term Evolution and UTRAN is short for Universal Terrestrial Radio Access Network. eMBMS was included in the Third Generation Partnership Project (3GPP) release 9 specifications. eMBMS is related to broadcasting of content to multiple users equipments simultaneously, utilizing LTE networks. eMBMS may for example be particularly useful during live events, such as music concerts or sports events, where millions of consumers are simultaneously viewing the same content, and where eMBMS may be used to broadcast complementary content, like different camera angles for instance, to LTE wireless devices. eMBMS enables operators to make better use of their available spectrum and free up network capacity. Thus, the operators may maximize efficiency when offering services such as live TV, video on demand, podcasts etc.
One concept in eMBMS is the MBSFN transmission, sometimes also referred to as multi-cell MBMS transmission using MBSFN operation or in a MBSFN area.
MBSFN is an MBMS Single Frequency Network. A MBSFN area comprises multiple cells in which transmission of identical waveforms is performed at the same time. A property of MBSFN transmission is that all participating cells transmit exactly the same content in a synchronized manner so it appears as one transmission to the wireless device. This gives the possibility for wireless devices to combine MBMS transmissions from multiple cells. Transmitting the same data to multiple wireless devices allows network resources to be shared. Mechanisms are therefore provided to ensure synchronization of the MBMS content—i.e. to ensure that all participating eNBs include the same MBMS control information and data in the corresponding time-synchronized subframe.
On the interface between the eNBs and the wireless devices, eMBMS introduces the logical channels MCCH and MTCH.
MCCH is short for Multicast Control CHannel and is a point-to-multipoint downlink channel used for transmitting MBMS control information from the eNB to the wireless devices. There is one MCCH for each MBSFN area.
MTCH is short for Multicast Traffic CHannel and is used for point-to-multipoint downlink transmission of MBMS user plane information from the eNB to the wireless devices. One MTCH is established in eMBMS for each eMBMS transmission/session.
A transport channel, MCH, is used to transport the MCCH and the MTCH(s), and a physical channel, PMCH, is used for transmitting the MCH. MCH is short for Multicast CHannel, and PMCH is short for Physical Multicast CHannel. There is a one-to-one mapping between the MCH and the PMCH.
The eMBMS is realized in the 3GPP specifications by the addition of a number of new capabilities to existing functional entities of the 3GPP architecture and by addition of a new functional entity, a Multi-cell/multicast Coordination Entity (MCE). According to 3GPP, there are two eMBMS deployment alternatives:                Alternative 1: Standalone MCE, see FIG. 1.        Alternative 2: Distributed MCE, see FIG. 2.Alternative 1        
Alternative 1 with the standalone MCE will now be described with reference to FIG. 1. FIG. 1 is an illustration of the eMBMS logical architecture of a wireless telecommunications network 100 with a standalone MCE.
The wireless telecommunications network 100 comprises a LTE core network 100a and a LTE radio access network 100b. The Broadcast Multicast Service Center (BM-SC) 101 is an entity which controls MBMS sessions and corresponding MBMS bearers.
In FIG. 1, the MCE 103 is a logical standalone entity. The functions of the MCE 103 are the admission control and the allocation of radio resources used by all eNBs 105 in the MBSFN area. Only two eNBs 105 are shown in FIG. 1 for the sake of simplicity, but the skilled person will understand that more than two eNBs 105 may also be comprised in the wireless telecommunications network 100.
The Mobility Management Entity (MME) 107 is a control node in the wireless telecommunications network 100. MBMS GateWay (MBMS GW) 110, is an entity that is present between the BM-SC 101 and eNBs 105 whose functions is the sending/broadcasting of MBMS packets to each eNB 105 transmitting the service. The MBMS GW 110 performs MBMS Session Control Signaling towards the E-UTRAN via the MME 107.
The content provider 113 provides eMBMS services to the wireless telecommunications network 100. The M3 115 is the interface between the MCE 103 and the MME 107, and is a control plane interface as indicated by the dotted line. M1 117 is the interface between the MBMS GW 110 and the eNBs 105, and is a user plane interface as indicated by the continuous line. M2 120 is a control plane interface between the MCE 103 and the eNBs 105. IP multicast 123 is used for point-to-multipoint delivery of user packets from the MBMS GW 110 to the eNBs 105.
It should be noted that according to this alternative, since the stand-alone MCE 103 controls the allocation of radio resources used by all eNBs 105 in the MBSFN area for the MBSFN transmission, the transmission of the allocation of radio resources to the wireless devices in the same MBSFN area is performed in the same manner by all eNBs 105.
Alternative 2
Alternative 2 with the distributed MCE will now be described with reference to FIG. 2. FIG. 2 is an illustration of the eMBMS logical architecture of a wireless telecommunications network 200 with a distributed MCE.
The wireless telecommunications network 200 comprises a LTE core network 200a and a LTE radio access network 200b. The Broadcast Multicast Service Center (BM-SC) 201 is an entity which controls MBMS sessions and corresponding MBMS bearers.
In this FIG. 2, the MCE is a distributed entity which is a part of another network element, i.e. the eNB. In FIG. 2, the combined MCE and eNB is referred to as an eNB/MCE 203.
Here, the Mobility Management Entity (MME) 207 is a control node in the communications network 200. The MBMS GW 210 is an entity that is present between the BM-SC 201 and eNB/MCE 203 whose functions is the sending/broadcasting of MBMS packets to each eNB/MCE 203 transmitting the service. The MBMS GW 210 performs MBMS Session Control Signaling towards the E-UTRAN via the MME 207.
The content provider 213 provides eMBMS services to the communications network 200. The M3 215 is the interface between the MCE part of the eNB/MCE 203 and the MME 207, and is a control plane interface as indicated by the dotted line. Thus, the architecture in FIG. 2 may be referred to as being a M3 based architecture. M1 217 is the interface between the MBMS GW 210 and the eNB part of the eNB/MCE 203 and is a user plane interface as indicated by the continuous line. IP multicast 223 is used for point-to-multipoint delivery of user packets.
In this alternative, the allocation of radio resources used by the distributed eNB/MCEs 203, i.e. multiple distributed MCEs where the multiple MCEs are co-allocated in eNBs, may be configured by another configuration node, such as, e.g. by an Operation Support Systems (OSS) node. It is then up to each of the eNB/MCEs 203 in the same MBSFN area to transmit the allocation of radio resources to wireless devices.
Unfortunately, it has been noticed that for the distributed eNBs/MCEs 203 receiving non-coherent allocations of radio resources from each of the eNB/MCEs 203 in the MBSFN area may result in failure in the reception of the MBSFN transmission at the wireless devices.